Effects of ultra-high-pressure annealing on characteristics of vacancies in Mg-implanted GaN studied using a monoenergetic positron beam.

Vacancy-type defects in Mg-implanted GaN were probed by using a monoenergetic positron beam. Mg ions were implanted into GaN to obtain 0.3-µm-deep box profiles with Mg concentrations of 1 × 1019 cm-3. The major defect species in an as-implanted sample was determined to be Ga-vacancy related defects such as a complex between Ga and N vacancies. The sample was annealed under a nitrogen pressure of 1 GPa in a temperature range of 1000-1480 °C without a protective capping layer. Compared with the results for Mg-implanted GaN annealed with an AlN capping layer, the defect concentration was decreased by the cap-less annealing, suggesting that the surface of the sample was an effective sink for vacancies migrating toward the surface. Depth distributions of Mg after annealing above 1300 °C were influenced by the presence of residual vacancies at this temperature. Hydrogen atoms were unintentionally incorporated into the sample during annealing, and their diffusion properties were also affected by both vacancies and Mg.

[Clinical application of neuroimaging to alcohol-related dementia].

Alcohol-related dementia (ARD) is one of the most common dementing disorders in middle-aged people and occurs in heavy drinkers who are estimated to be 10 - 15 % of the adult men in a community. While the concept of ARD is multifactorial and includes all cognitive deficits in alcoholics, the central clinical manifestations are exemplified by Korsakoff's syndrome (KS), a persistent neuropsychiatric syndrome, characterized by amnesia and disorientation that is caused by thiamine deficiency along with excessive alcohol consumption. Antemortem detection of intracranial changes has been made possible by MRI and many studies have revealed that alcoholics have atrophic changes in frontal lobe, cerebellum, medial temporal lobe and hippocampus. However, these brain regions are vulnerable to excessive alcohol and seem to be independent of cognitive deficits in alcoholics. This review shows the regional differences in gray matter volumes between cognitively normal alcoholics and patients with KS. By employing a 3-dimensional MRI method for voxel-based morphometry that enables an automated, unbiased, comprehensive assessment, we demonstrate that parahippocampal/hippocampal atrophy is specific to KS and thalamic atrophy and the third ventricle enlargement are more severe in patients with KS than in cognitively normal alcoholics.

Synthesis and pharmacological profile of serofendic acids A and B.

We present efficient syntheses of serofendic acids A and B (SA-A and SA-B), novel neuroprotective substances isolated from fetal calf serum. Biological and pharmacological evaluation showed that SA-A and SA-B have potent protective action against glutamate-induced neurotoxicity, but do not interact directly with glutamate receptors. A pharmacokinetic study showed that they have good oral bioavailability in rats. The results indicate that SA-A and SA-B are potential lead compounds for candidate drugs to treat various neurological disorders.

Amphiphilic polysilane-methacrylate block copolymers - Formation and interesting properties.

Several polysilane block copolymers have been prepared by the newly developed method, anionic polymerization of masked disilenes. Especially amphiphilic block copolymers of poly(1,1-dimethyl-2,2-dihexyldisilene) and poly methacrylate are focused. Poly(1,1-dimethyl-2,2-dihexyldisilene)-b-poly(2-hydroxyethyl methacrylate) (PMHS-b-PHEMA) is the first example of the amphiphilic polysilane copolymer that can form micelles in polar solvents. Poly(1,1-dimethyl-2,2-dihexyldisilene)-b-poly(methacrylic acid) (PMHS-b-PMAA) is more polar than (PMHS-b-PHEMA), soluble in water to form micelles. The cross-linking reaction of (PMHS-b-PMAA) with 1,10-diaza-4,7-dioxadecane and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride afforded the first shell cross-linked micelles (SCM) of polysilane. In addition to interesting properties, SCM is indicated to be able to form hollow sphere particles (hollow shell cross-linked micelles, HSCM) by a photochemical process. Reversible encapsulation of guest molecules by SCM and HSCM is demonstrated. Finally, SCM can be used as the template for the synthesis of metal nanoparticles, which may be used as catalysts.

Induction of optical activity in oligosilanes within the internal cavity of cyclodextrins.

The first example of induced optical activity of oligosilanes within the internal cavity of gamma-cyclodextrins is reported.

Diastereoselective addition of alcohol to diastereotopic silylenes.

The successful example of diastereoselective addition of alcohol to diastereotopic silylenes is reported.

Synthesis and Characterization of the Dilithium Salt of the Octasilyl[4]radialene Dianion: Evidence for a Lithium Walk on the Eight-Center, Ten-Electron π-Electron System.

A highly symmetric structure is displayed in toluene by 1, which was obtained by reduction of octasilyl[4]radialene with lithium in THF. The two Li+ ions of 1 are not fixed to the π-electron system in toluene, but are fluxional, giving rise to a bis-contact ion pair. In a solvating medium such as THF, one of the Li+ ions dissociates in such a way that 1 exists as a contact ion pair and a solvent-separated ion pair.